This invention relates to methods for separating solid lubricating materials used in drilling operations from the cuttings generated by such drilling operations.
In drilling operations, a drilling mud is often employed to remove the chips or cuttings produced by the rotating drill bit and to reduce friction or provide a lubricating medium for the drill bit and drill pipe. In operation, the drilling mud is pumped down the drill pipe, through the drill bit where it picks up the cuttings and is returned to the surface between the drill pipe and the wall of the well bore. The drilling mud containing the cuttings is then conventionally fed through a shale shaker which removes the larger size cuttings, e.g, particles larger than about 50 mesh. The recovered mud, i.e., that mud which passes through the shale shaker, is reused in the drilling operation. By-passing the shale shaker is undesirable in that the drill cuttings are recirculated down the well where they are reground by the bit and dispersed in the drilling mud. This results in an undesirable viscosity increase in the drilling mud, requiring frequent dilution and reweighting of the mud with other additives.
In many drilling operations, particularly directional drilling operations, the drill pipe contacts the wall of the well bore. The drag created by such contact increases the torque required to rotate the drill pipe at a fixed rate. As these points of contact increase, the torque required to drive the drill pipe increases to a maximum level above which further increases in torque would probably break the drill pipe. Thus, the rate at which the drill pipe is rotated must be reduced to maintain the torque at or below this maximum. Unfortunately, this rotation rate reduction generally creates a less efficient drilling operation.
To reduce this drag, a hard, particulate material is often added to the drilling mud as a lubricating material. This particulate material provides a rolling support for the drill pipe at its points of contact with the walls of the well bore, thereby reducing the torque required for effective drilling.
Particulate materials which have been found to be particularly useful as solid lubricating materials are known to possess a size in the range from 10 to 100 mesh and a relatively uniform shape, preferably spherical. See, for example, U.S. Pat. No. 2,943,679 to Scott and Fischer and U.S. Pat. No. 4,063,603 to Rayborn.
Unfortunately, many of the solid lubricating particles, e.g., the particles of greater than 50 mesh size, are removed from the drilling mud during the recovery of the drilling mud in the shale shaker operation. Heretofore, the solid lubricating particles thus removed could not be readily recovered for reuse.
In view of these deficiencies, it is highly desirable to provide a method of separating the solid lubricating particles from the drill cuttings which have not passed through the shale shaker with the drilling mud.